The invention relates to dental compositions, and more specifically, to polymerizable dental compositions, and more specifically to polymerizable dental compositions containing multifunctional acrylate compounds that are polymerizable by use of a light emitting diode (“LED”) and other light sources, and cure without an oxygen inhibited layer, and with reduced or no unwanted yellow cast. In general, dental sealants and adhesives are widely used in clinical settings. Desirable properties include safety, efficacy, durability, and favorable cosmetic properties. It is preferred that dental compositions be shelf stable, easy to formulate, and that they do not set so rapidly as to make them difficult to apply to a patient.
Dental compositions frequently contain monomers which are polymerized by the dentist or technician (e.g. by light, self-cure, or dual-cure). However, many dental compositions form a problematic “oxygen inhibited layer” (OIL) or “uncured layer” on their surface. This layer's polymerization is inhibited due to the presence of molecular oxygen in ambient air. As a result, incomplete polymerization occurs, causing the surface to be sticky or tacky, leading to lower hardness of the surface and/or no curing if a thin surface is present.
Several attempts have been made to provide a dental composition which cures completely and without the problematic uncured layer. Such compositions include a composition known as “Extoral,” a visible-light cured dental resin formulation sold by AFR Imaging Corp. (Portland, Oreg.). Extoral cures rapidly and produces a glossy, hard (but brittle) surface upon irradiation with a normal dental curing light. While the composition of Extoral is proprietary and not publicly known, its odor belies the presence of methyl methacrylate. The strong odor is objectionable to both patients and dentists/technicians, making it difficult to use in a laboratory, and nearly impossible to use in a clinical setting.
In response, U.S. patent application Ser. No. 10/224,795 (incorporated herein by reference) relates to a dental composition lacking an oxygen inhibited layer and lacking a strong odor associated with volatile compositions. Therefore, U.S. patent application Ser. No. 10/224,795 discloses a dental composition which cures completely, and does so without the offensive odors seen in earlier compositions. Such compositions work well with halogen or other light source curing units, but do not quickly cure without an oxygen inhibited layer when exposed to dental LED light curing units. LED light units have recently become more popular due their long service time, difference in the effective spectrum emitted, and portability of the units. While the abovementioned patent application discloses the use of a dental composition with Camphorquinone (“CQ”) or CQ and amine complexes or systems as a photoinitiator to produce hard curing, high gloss composition without an oxygen inhibited layer, these photoinitiators have a drawback in certain applications that has precluded their use dental compositions. More specifically, it was observed that the relatively high concentrations of CQ and amine used in the present invention with LED light curing sources to provide a no-oxygen inhibited curing created a pronounced yellowish tint in the cured resin after the resin initiator system was subjected to a curing irradiation. This is in contrast to prior art teachings of the use of CQ and CQ-amine systems at low concentrations alone or in combination with colored dyes or other photobleachable colorant compositions that lose their initial color during the curing irradiation process. See, e.g., U.S. Pat. No. 6,528,555 at Table 1 and at Col. 4, lns. 51-60, Col. 5, lns. 3-9, and Col. 8, lns. 46-50.
In order to create a CQ or CQ and amine system dental composition that quickly cures under dental LED light curing units without an oxygen inhibiting layer, the levels of CQ or CQ and amine system must be very high—thereby imparting a nearly fluorescent yellow cast to any restorations made with such a dental composition. Thus, while increased levels of CQ or CQ and amine system allow a dental composition to quickly cure under LED light curing units, and over a broader range of wavelengths, increased levels of CQ and a CQ and amine system have not been used in dental compositions due to their cosmetic deficiencies. Certainly, the use of CQ and a CQ and amine system in high quantities severely limits the application of such compositions comprising them, as extremely yellow dental restorations are cosmetically unacceptable in most applications. Therefore, an LED curable dental composition that cures without an oxygen inhibited layer and without a distinctive yellow cast would be greatly appreciated in the art.
While photobleachable dyes have been used in dental compositions in conjunction with CQ and a CQ and amine system, those systems actually add a colored dye to the composition that will disappear when a light is applied. See, e.g. U.S. Pat. No. 6,528,555 at Col. 4, 1.50-Col. 5, 1.10. Further, while the dye is photobleachable, the color imparted by the CQ or CQ and amine system remains. In short, it is known to use a complex initiator/dye system using CQ in combination with a photobleachable colorant or dye that imparts a vibrant initial color to the dental composition to assist in visualization of the application of the composition to the dental surface, wherein the dye loses some or all of this vibrant color during irradiation of the composition. This reference teaches against the use of CQ or CQ and amine initiator systems alone, and does not disclose reducing oxygen inhibition of the overall curing process through use of high concentrations of CQ or CQ and amine systems. As such, the use of photobleachable dyes fails to reduce yellowing inherent in the use of high concentrations of CQ or CQ and amine systems during their irradiation.
Therefore, it would be of great value to develop a dental composition and method that allows a dental restoration to be cured to a hard, scratch free surface without an oxygen inhibited layer, while at the same time reducing or eliminating the extreme yellow cast that is imparted through the use of CQ and amine photoinitiator system. Further, providing a composition that cures with reduced or no discoloration and/or with visible light across several different wavelengths, and which can be effectively and quickly cured without an oxygen inhibited layer using a standard dental LED light curing unit would be greatly appreciated.